In general, the term “organic light emitting phenomenon” refers to a phenomenon in which electric energy is converted to light energy by means of an organic material. The organic light emitting device using the organic light emitting phenomenon has a structure usually comprising an anode, a cathode and an organic material layer interposed therebetween. Herein, the organic material layer may be mostly formed in a multilayer structure comprising layers of different materials, for example, the hole injecting layer (HIL), the hole transporting layer (HTL), the light emitting layer (EML), the electron transporting layer (ETL), the electron injecting layer and the like, in order to improve efficiency and stability of the organic light emitting device. In the organic light emitting device having such a structure, when a voltage is applied between two electrodes, holes from the anode and electrons from a cathode are injected into the organic material layer, the holes and the electrons injected are combined together to form excitons. Further, when the excitons drop to a ground state, lights are emitted. Such the organic light emitting device is known to have characteristics such as self-luminescence, high luminance, high efficiency, low drive voltage, wide viewing angle, high contrast and high-speed response.
However, the conventional organic light emitting devices have problems that they have large difference in the work functions between the electron transporting layer and the cathode material, which does not allow easy electron injecting, and a relatively large amount of holes are injected toward the cathode, which lowers the light emitting efficiency. LiF has been widely used as the materials of the electron injecting layer provided between the electron transporting layer and the cathode, but the material has no hole blocking ability.